As semiconductor devices have become more highly integrated in recent years, circuit interconnections have become finer and distances between those circuit interconnections have become smaller. For example, in photolithography, it is desirable that surfaces on which pattern images are to be focused by a stepper should be as flat as possible because the depth of focus of the optical system is relatively small. Chemical mechanical polishing (CMP) has been developed to planarize layers on semiconductor wafers for processes such as photolithography.
A typical chemical mechanical polishing apparatus comprises a polishing table having a polishing pad (polishing cloth) attached to an upper surface of the polishing table, and a top ring for holding a substrate to be polished, such as a semiconductor wafer. The polishing table and the top ring may be rotated at independent rotational speeds. The top ring presses the substrate against the polishing pad under a predetermined pressure. A polishing liquid (slurry) is supplied from a polishing liquid supply nozzle onto the polishing pad. In this manner, a surface of the substrate is polished to a flat mirror finish.